Method and system for petroleum recovery



P 995011 XR 3 2569935 June 21, 1966 'w, NABQR ETAL 3,256,935

METHOD AND SYSTEM FOR PETROLEUM RECOVERY Filed March 21. 1963 aSheets-Sheet 1 Q 13. -v-r' r? .|2 I2 I l2. 7 v a I u I f f FIG. I;

GEORGE w. mason MOHAMED MORTADA 1 INVENTORS,

E Y v V v WWI-6W I E ATTORNEY.

r Mm

June 21, 1966 'QwNABQR ETAL 3,256,935

METHOD AND SYSTEM FOR PETROLEUM RECOVERY i Filed March 21, 196: asheets-sheet 2' 1i F *7 I 16 a :6 d I6 I f r 7 7 l6 l6 l6 l7 6 lg lg I5I77 GEORGE w. mason MOHAMED MORTADA INVENTORS BYM 8W ATTORNEY June 21,1966 s. w. NABOR ETAL 3,256,935

METHOD AND SYSTEM FOR PETROLEUM RECOVERY Filed March 21, 1963 u ssums-sheet s v use w.- mean oumcu MORTAOA INVENTGRQ- I MLQM ATTQRNEYUnited States Patent ice This invention relates to a method, and asystem, for petroleum recovery from subterranean reservoirs. Moreparticularly, it relates to the primary recovery of,petroleum fromanisotropically permeable reservoirs.

Many methods and systems for recovering petroleum from subterraneanreservoirs are known and used. Generally, the rates and extents ofpetroleum recovery from isotropically permeable reservoirs by suchmethods and systems are satisfactory. One reason for this is the factthat the uniform flow of fluids in isotropically permeable reservoirsproduces circular drainage patterns about each petroleum recovering orproducing well. For this reason, isotropically permeable reservoirs areproduced by means of a plurality of. wells disposed in regular, uni

. form, geometric well patterns extending over the reservoir. In thegeometric well patterns, the wells are cated in the reservoir instraight parallel lines or rows.

The rows of wells are equally or uniformly spaced from one another.equally or uniformly spaced from one another. The magnitude or distanceof the spacing between rows of wells, and between wells in a row,.willvary with the geometric well pattern used. Usually, the primary factorto be considered in determining the actual magnitude of the spacingbetween rows and wells in any geometric well pattern is the circulararea to be drained by each well. Thus, as an example, each well may beplaced on from about each 3 to about each 40 acres.

There are many advantages in using geometric patterns of wells toproduce isotropically permeable reservoirs. One advantage is that thewells may be readily located to cover the reservoir. Another advantageis that less wells are needed for optimum petroleum recovery. Theprimary basis of these advantages is that each well can continueproducing petroleum at full production rates untilits circular drainagepattern expands sufliciently to meet or interfere with the drainagepattern of one or more of its neighboring production wells. Onceinterference between drainage patterns occurs, the production ratesof'the concerned production wells decrease. However, with the regular,uniform, geometric well patterns, the areas of the reservoir notwithinthe circular drainage patterns at the onset of interference arevery small compared to the areas within the circular drainage patterns.This results in substantial and efficient recoveries of the availablepetroleum in the reservoir.

It would be desirable 'to use the regular, uniform, geometric wellpatterns to recover petroleum from uniformly anisotropically permeablereservoirs. These are reservoirs in which the permeability variesaccording to direction. In these reservoirs, the fluids will flowthrough the formation in greater amounts in certain directions. As aresult, the drainage pattern of each petroleum producing well will benoncircular. For this reason, the

Further, the wells in each of the rows are Patented June 21, raceinitial interference to a reservoir with meability.

It is therefore an object of the present invention to provide a method,and a system, for petroleum recovery from oil-bearing reservoirs.

Another object of this invention is to recover petroleum fromanisotropically permeable reservoirs.

Another object of this invention is to use regular, uniform, geometricwell patterns in recovering petroleum from anisotropically permeablereservoirs.

Another object of this invention is to use the direcisotropic pertionalpermeability of an oil-bearing reservoir to increase the recovery ofpetroleum.

Another object of this invention is to use regular, uniform, geometricwell patterns for producing petroleum from anisotropically permeablereservoirs without an early decrease in production rates due to thepermature onset of interference between the drainage patterns fromadjacent wells.

Another object is to use a regular, uniform, geometric well pattern forrecovering petroleum from anisotropically permeable reservoirs whereinthe production rates can be maintained for a longer period of timebefore being decreased by interference between the drainage patternsabout the wells.

These and other objects will become more apparent when read inconjunction with the following description and the attached drawings ofone illustrative embodiment of the present invention, where in thedrawings:

FIGURE 1, FIGURE 2, and FIGURE 3 show several different regular,uniform, geometric well patterns;

regular, uniform, geometric well patterns have failed to I producetheadvantageous results in anisotropically per- FIGURE 4 shows thegeometric well pattern of FIG- URE l in an isotropically permeablereservoir at the onset of interference between the well drainagepatterns;

FIGURE 5 shows the geometric well pattern of FIG- URE 4 at the onset ofinterference between well drainage patterns in areservoir havinganisotropic permeability; and

FIGURE 6 shows a geometric well pattern inaccordance with the presentinvention at the onset of interference of well drainage patterns in theanisotropically permeable reservoir of FIGURE 5.

The method and system of this invention are provided by means of aplurality of petroleum producing wells arranged in a novel, regular,uniform, geometric well pattern. In the geometric well pattern the wellsare arranged in several equally spaced parallel rows aligned with thedirection of greatest permeability. The wells are disposed at a uniformspacing ineach row. The ratio of the distance between adjacent wells ineach row to the perpendicular distance between adjacent rows isproportional to the square root of the ratio of permeability in thedirection of greatest permeability to the least permeability.

Referring now to the drawings, in FIGURES 1 through 5, there are shownknown systems of wells for recovering petroleum from isotropicallypermeable reservoirs by means of wells'located in regular, uniform,geometric well patterns which are conventional. In FIGURE 1 there isshown a geometric well pattern which may be described as a rectangularor square pattern. The reservoir 11 is penetrated by a plurality ofwells 12 which shown in FIGURE 4.

16 are arranged at an equal spacing d between adjacent wells 16 in eachof the parallel rows 17. The rows 17' are arranged at an equal spacinga. Spacing a is taken perpendicularly between the rows 17. The spacing ain the pattern in FIGURE 2 is one-half the spacing d. Further, eachalternate row is shifted parallel to the remaining rows by one-half thespacing d. The ratio of d to a is 2 in the staggered line geometric wellpattern in FIG- URE 2.

Another conventional staggered line geometric well pattern is shown inFIGURE 3. This geometric pattern may be described as the hexagonalpat-tern. The hexagonal pattern provides a system of wells in which thewells are accurately staggered at a uniform distance from one another.Thus, any three adjacent wells form the ap'exes of an equilateraltriangle. tween the wells is the same throughout the geometric wellpattern. In the hexagonal pattern, shown in FIGURE 3, a plurality ofwells 21 penetrate the reservoir 11. The

wells 21 are arranged at an equal spacing d between adjacent wells 21 ineach of the parallel rows 22. The rows 22 are arranged at an equalspacing a. Spacing a is taken perpendicularly between the rows 22. Eachalternate row is shifted parallel to the remaining rows 22 by onehalf ofthe spacing d. Since each adjacent three wells 21 form the apexes of anequilateral triangle in the hexagonal pattern, the ratio of d to a is 2/3.

Thus, it will be apparent that in any regular, uniform, geometric wellpattern the wells penetrating the reservoir are located in straightparallel rows. Further, the adjacent wells in each row are equallyspaced. Also, the rows of wells are uniformly spaced from one another.The ratio of d to a will be determined by the particular spacing ofwells and rows of wells in regular, uniform, geometric well patternswhich are conventional. As a result, only the exact magnitudes of thespacings d and a will be contingent upon the area to be drained by eachwell in any conventional geometric well pattern.

As an example of the above, the system of wells provided by therectangular geometric well pattern shown in FIGURE 1 often is used inconventional methods of recovering petroleumfrom an isotropicallypermeable reservoir. The results are shown in FIGURE 4. The wells 12 areprovided with suitable means for recovering petroleum from reservoir 11.Such means are well known and need not be described herein. As thepetroleum in the reservoir 11 is produced at equal rates through wells12, circular drainage patterns 31 are established as a result of theisotropic permeability of the reservoir 11.

-The circular drainage patterns 31 are illustrated by the shaded areas.The drainage patterns 31 progressively expand at relatively constantrates of petroleum recovery. The constant rates of petroleum recoverywill be maintained until the adjacent drainage pat-terns 31 meet asOnset of interference between drainage patterns 31 then begins. Theproduction rates of petroleum through wells 12 decreases as a result ofsuch interference. However, the petroleum remaining in the reservoir 11,as represented by the unshaded areas, is very small. Thus, one advantageof using a system of wells located in a geometric well pattern inisotropically permeable reservoirs is that substantially all of the areain the reservoir is drained of at least some petroleum before the onsetof interference between the circular drainage patterns 31 occurs.

Attempts to use a system of wells of a conventional, geometric patternin methods of recovering petroleum from reservoirs exhibitinganisotropic permeability produce less favorable results than, theresults obtained in isotropically permeable reservoirs. For example, thesystem of wells of the square geometric well pattern of FIG- URE 4 inconventional methods of petroleum recovery in an anisotropicallypermeable reservoir produces results illustrated in FIGURE 5. FIGUREshows a reservoir 41 which. for example, has a permeability in thedirection The distance or spacing be-.

of greatest permeability three times as great as the permeability in thedirection of least permeability. The direction of greatest permeabilityis indicated by chainline 42.

The reservoir 41 may be considered to be of uniform thickness andporosity. Also, the permeability may be considered to be uniformlyanisotropic with each principal axis of permeability maintaining thesame direction and magnitude at every point in the reservoir 41. Two ofthe principal axes of permeability lie in the bedding plane at rightangles to one another. The third axis of permeability is normal to thebedding plane. Usually, the force of gravity may be neglected so thatthe anisotropic permeability comprises the permeability oriented indirections along the bedding plane.

As the petroleum is produced at equal rates through wells 43,noncircular drainage patterns 44 are established as a result of theanisotropically permeable character of the reservoir 41. The noncirculardrainage patterns are illustrated by shaded areas. The noncirculardrainage patterns 44 progressively expand with the production ofpetroleum from the reservoir 41 until the adjacent patterns meet, asshown in FIGURE 5. Onset of interference between the noncirculardrainage patterns 44 then begins. As a result of such interference, therates of petroleum recovered through wells 43 decrease. Further, theinterference between drainage patterns 44 is premature. The drainagepatterns 44 meet along one direction, but are spaced apart by asubstantial distance in a normal direction. This can be readily seenfrom FIGURE 5 where the shaded areas in the reservoir 41 from whichpetroleum has been recovered are relatively much smaller than the areasavailable for production when compared under the same conditions of theonset of interference to a reservoir having isotropic permeability, asseen in FIG- URE 4.

Referring now to FIGURE 6, an illustrative embodiment of a method, and asystem, of the present invention will be given. 'The reservoirs 41 ofFIGURES 5 and 6 are considered to be the same, with the same anisotropicpermeabilities and directions. One regular, uniform, geometric wellpattern will be described for use, in accordance with this invention, inthe reservoir 41 as a method for recovering petroleum. Similarly, asystem of wells for recovering petroleum will also be described.

In the practice of the method of this invention, the direction andmagnitude of greatest permeability and the magnitude of leastpermeability must be known. In some instances, this information isavailable. However, where this information is not available,determination of the direction and magnitude of greatest permeabilityand the magnitude of least permeability will be the first step in themethod of this invention. The permeability magnitudes and theirdirections may be determined by any suitable means. For example, corestaken from various portions of the reservoir are analyzed to determinethe directions and ratios of the greatest and least permeabilities.Another means to obtain this information is by fluid injection in onewell and measuring the pressure or fluid flow increase in thesurrounding wells. Other means to obtain this information will beapparent to those skilled in the art.

The direction of greatest permeability is shown by chain-line 42. As anexample, the permeability in the direction of greatest permeability hasa relative value of 3. The least permeability has a relative value of 1.

Another step is to provide a plurality of petroleum recovering wells 47penetrating the reservoir 41 in a novel, geometric well pattern. Thewells 47 may be drilled or selected from wells in existence, or providedby a combination of both. In a compilation of such wells 47, any wellsnot needed in the novel, geometric well pattern in this invention may beshut-in. The wells 47 are arranged in several equally spaced parallelrows 45. These rows 45 are aligned substantially with the direction ofgreatest permeability as illustrated by chain-line. 42. The wells 47 aredisposed at a uniform spacing between adjacent wells '47 in each row 45.Further, as part of this step, the spacing d between wells 47 and thespacing a between rows 45 is proportioned in the following particularmanner. Particularly, the spacing of the wells in a row and between rowsprovides a ratio of d to a proportional to the square root of the ratioof the permeability in the direction of greatest permeability to theleast permeability. A new geometric well pattern can be developed withthe desired proportion of dto a by selecting the desired area to beproduced by each well. I

If desired, any conventional, regular, uniform well pattern canbe-adapted to provide the desired proportion of d to a. Any conventionalgeometric well pattern is adapted to reservoir 41 by placing the wellsat new spacing ratio of d to a, which new spacing ratio is substantiallyequal to product of the ratio of d to a of the original geometricpattern and the square root of the ratio of the permeability in thedirection of greatest permeability to the least permeability. Forexample, the square pattern of FIGURE 5 wherein the ratio of d to a isunity can be adapted to provide a greatly improved petroleum recov-- cryfrom reservoir 41. This result is obtained by placing wells 47 in rows45 with the ratio of d to a in the novel, geometric well patternsubstantially equal to the' product of the ratio of d to a of the squarepatterriand the square root of the ratio of 3 to 1. Therefore, inaccordance with the present invention, the conventional square,geometric well pattern becomes a rectangular geometric well patternwherein the ratio of the distance between wells 47 in each row 45 to thedistance, taken perpendicularly between adjacent rows 45 issubstantially equal to the square root of 3. It will be apparent thatany regular, uniform, geometric pattern can be used in this invention.

If the rows of wells 43 in the square pattern of FIG- URE 5 were alignedwith the direction of greatest permeability, premature onset ofinterference between the drainage patterns about the wells would occurbecause the drainage pattern 44 would meet along a direction inalignment with chain-line 42 before any substantial area of thereservoir 41 was produced. For this reason, by this invention, the-ratioof d to a of any known or designed geometric pattern desired to be usedin reservoir 41 is adapted to provide drainage patterns which do notproduce premature onset of interference with all the resultant undesiredresults.

The system of wells 47 located in this manner-in reser- With 41 permitsconventional methods of recovering petroleum to increase the duration ofthe petroleum recovery rates before a decrease therein occurs. Also, itenables such methods to recover petroleum from larger areas of thereservoir than otherwise. Further, the area drained by each well can beas great, if not greater, than in the conventional, regular geometricpattern.

The wells 47 are provided with suitable means for recovering petroleumfrom reservoir 41. As'the petroleum is produced at equal rates throughwells 47, noncircular drainage patterns 46 develop about these wells.The noncircular drainage patterns 46 steadily increase in size untilthey meet, as seen in FIGURE 6, as illustrated by the shaded areas.Interference between patterns 46 then begins. However, the improvementto petroleum recovery is evident upon comparing the drain: age patterns44 of FIGURE 5 with the drainage patterns 46 of FIGURE 6. The areas ofthe reservoir 41 covered by drainage patterns 46 at the onset ofinterference are very large compared to the areas left for petroleumrecovery. Further, the areas covered by the drainage patterns 46 aremuch larger than the areas covered by the drainage patterns 44 of FIGURE5 under the same reservoir conditions and method of petroleumproduction.

Thus, by the present invention we have provided a method for recoveringpetroleum from anisotropically permeable reservoirs using a system ofwells in regular, uniform, geometric well patterns. The method, and thesystem, do not suffer from the undesired results produced by usingmethods and systems of the prior art, as illustrated by FIGURE 5.

The results are obtained in the present invention by equidistant spacingbetween wells in each row and by equidistant perpendicular spacingbetween adjacent rows. Thus, any regular, uniform, geometric wellpattern can be used. The present invention is also of utility where thespacings between wells, and between rows, may vary. However, the resultsobtained will be somewhat less than would be obtained in an exactinglyuniform spacing be tion entitled An Approximate Method for DeterminingAreal Sweep Efficiency and Flow Capacity in Formations with AnisotropicPermeability in the December 1961 issue of Society of PetroleumEngineers at pages 277-286.

From the foregoing description, an illustrative embodiment of a method,and a system, has been set forth satistying the objects of thisinvention. Various changes can be made to the method, and the system, bypersons skilled in the art without departing from the intent of theinvention. It is intended that such changes be recognized as beingwithin the scope of the appended claims.

What is claimed is: f

l. A method for petroleum recovery from an oil-bean ing subterraneanreservoir exhibiting anistropic permeability comprising the steps of:

(at) determining the direction and magnitude of greatest perrneabilityand the permeability in the direction of least permeability,

(b) providing a plurality of petroleum recovering wells penetrating thereservoir disposed in a geometric pattern where in such pattern thewells are arranged in several equally spaced parallel rows aligned withthe direction of greatest permeability with the wells disposed at auniform spacing in each row, and theratio of the distance betweenadjacent wells in a row to the perpendicular distance between adjacentrows of wells is proportional to the square tion of least permeability,and v (b) providing a plurality of petroleum recovering jwellspenetrating the reservoir disposed in a geometric pattern where in suchpattern the wells are arranged in several equally spaced parallel rowsaligned with the direction of greatest permeability with the wellsdisposed at a uniform spacing in each row, and the ratio of the distancebetween adjacent wells in a row to the perpendicular distance betweenadjacent rows of wells is substantially equal to the product. of thedistance between adjacent wells in each row and the perpendiculardistance between adjacent rows of wells of a conventional geometricpattern to be adapted for use in the reservoir, and the square root ofthe ratioot the permeability in est permeability and the permeability inthe dircc the direction of greatest permeability to the leastpermeability.

3. The method of claim 2 where in the conventional geometric pattern tobe adapted for use in the reservoir the ratio of the distance betweenadjacent wells in a row to the perpendicular distance between adjacentrows of wells is unity.

4. The method of claim 2 where in the conventional geometric patterntobe adapted for use in the reservoir the ratio of the distance betweenadjacent wells in a row to the perpendicular distance between adjacentrows of wells is 2.'

' 5. The method of claim 2 wherein the conventional geometric pattern tobe adapted for use in the reservoir the ratio of the distance betweenadjacent wells inta row to the perpendicular distance between adjacentrows of 'wells is 2V3:

References Cited by the Examiner CHARLES E. O'CONNELL, Primary Examiner.

C. H. GOLD, ZALENSKI, Assistant Examiners.

1. A METHOD OF PETROLEUM RECOVERY FROM AN OIL-BEARING SUBTERRANEANRESERVOIR EXHIBITING ANISTROPIC PERMEABILITY COMPRISING THE STEPS OF:(A) DETERMINING THE DIRECTION AND MAGNITUDE OF GREATEST PERMEABILITY ANDTHE PERMEABILITY IN THE DIRECTION OF LEAST PERMEABILITY, (B) PROVIDING APLURALITY OF PETROLEUM RECOVERING WELLS PENETRATING THE RESERVOIRDISPOSED IN A GEOMETRIC PATTERN WHERE IN SUCH PATTERN THE WELLS AREARRANGED IN SEVERAL EQUALLY SPACED PARALLEL ROWS ALIGNED WITH THEDIRECTION OF GREATEST PERMEABILITY WITH THE WELLS DISPOSED AT A UNIFORMSPACING IN EACH ROW, AND THE RATIO OF THE DISTANCE BETWEEN ADJACENTWELLS IN A ROW TO THE PERPENDICULAR DISTANCE BETWEEN ADJACENT ROWS OFWELLS IS PROPORTIONAL TO THE SQUARE ROOT OF THE RATIO OF THEPERMEABILITY IN THE DIRECTION OF GREATEST PERMEABILITY OF THE LEASTPERMEABILITY, AND (C) RECOVERING PETROLEUM FROM THE RESERVOIR THROUGHSUCH WELLS FOR DISPOSAL AT THE SURFACE OF THE EARTH.